1. Field of the Invention
The present invention relates to a non-invasive automatic blood pressure measuring apparatus for non-invasively detecting the maximal blood pressure and the minimal blood pressure in the depressing process after attaching a cuff at a part of the body and compressing.
2. Description of the Prior Art
In this kind of automatic blood pressure measuring apparatus, there are two kinds of apparatuses; a first type which detects Korotkov sounds by a microphone in the depressing process and measures the internal pressure of the cuff at the start and the termination of this sound according to the Korotkov sound recognizing method, and a second type which detects a pulse wave caused by the pulsation of the artery as a vibration upon the internal pressure of the cuff and measures the blood pressure based on the change of this vibration according to an oscillometric method.
However, the apparatus of the former method is easily affected by noises. In addition, there is a problem in its measuring precision because there are cases that Korotkov sounds sometimes fade away or do not fade out even if blood pressure is minimal. In the latter method, although the problems caused by the lack of stability of the generation of Korotkov sounds have been solved, there still remains a problem with its measuring precision: since the pulse wave is detected as an internal pressure change in the cuff, the pulse waves contacting the cuff at different points varied in the direction of the width of the cuff are detected with add operation. In addition, since the detection of minimal blood pressure from the vibration itself is difficult, and it is supposed from the operation using the mean value of the blood pressure, a problem also remains in its measuring precision.